Nitrogen 1 Flashcards
What do amino acids and nucleotides contain that carbohydrates and fats don’t?
Nitrogen
Where does the nitrogen in our bodies come from?
Our diets
How do the plants/animals we eat get their nitrogen?
From nitrogen fixing bacteria known as the diazotrophs.
What are the 3 stages called in the nitrogen cycle?
- Fixation
- Assimilation
- Degradation
What is the structure of nitrogen?
2 nitrogen atoms are held together by triple bond making it very unreactive
How can nitrogen be captured?
- Adding oxygen using lightening to form NO or NO2
- Adding hydrogen using the Haber process to form NH4
What are 2 examples of nitrogen-fixing bacteria?
- Cyanobacteria found in Lake Atitlan
- Rhizobium bacteria found on root nodules of legumes
What do bacteria require for nitrogen fixation?
- Nitrogenase
- Energy
What does the fixation of nitrogen produce?
Un-ionised ammonia (NH3) which in water will exist in equilibrium with ionised ammonium (NH4+)
What inactivates nitrogenase?
Oxygen
How do nitrogen fixing bacteria get around the abundance of oxygen?
- Live anaerobically
- Some uncouple mitochondria which increases electron flow and ‘burns’ off O2 in the cell
How do cyanobacteria prevent O2 entry?
Form heterocysts whose cell walls prevents O2 entry
How do leguminous plants allow nitrogenase to work?
They produce leghemoglobin which binds to O2 and keeps the concentration low enough
What happens after nitrogen is fixed?
- Soil bacteria convert ammonia to nitrite and then to nitrate.
- Nitrate is taken up by plants and micro-organisms
- Once the nitrate has been taken up it is then converted back to ammonia via nitrite
What is the only amino acid that can obtain its nitrogen directly from NH4 and the only one which cn give it up directly?
Glutamate
What are the 4 amino acids which are found in higher concentration in cells compared to other amino acids
- Alanine
- Glutamine
- Glutamate
- Aspartate
What are the roles of glutamate?
- Excitatory neurotransmitters
- Important in taste
- Amino acid breakdown
What is transamination?
Conservation of nitrogen by transferring amino groups between different molecules
What are the general principles of transamination?
- No loss or gain of nitrogen
- Readily reversible
- One of the 2 substrate pairs is often glutamate
- Amino acid 1+ Keto acid 2= Keto acid 1+ Amino acid 2
What is the difference between an amino acid and a a-keto acid?
- Amino acid has an NH3 group attached to a carbon which is attached to a COOH group
- a-Keto acid has a C double bond O attached to the acidic group
What does the reversible nature of transamination allow it to do?
Participate in amino acid synthesis and degradation
What do all aminotransferases rely on?
Pyridoxal phosphate cofactor
What typically accepts amino groups?
a-ketoglutarate
What acts as a temporary storage of nitrogen?
L-glutamine
What can L-glutamine do?
Donate the amino group when needed for amino acid biosynthesis
What is pyridoxal phosphate?
-Cofactor made from vitamin B6
What does pyridoxal phosphate do?
Transfers the amino acid group during the reaction
What does the presence of aminotransferases in the plasma indicate?
Cell damage as they are intracellular proteins
What aminotransferases are particularly good indicators of cell damage
- Aspartate aminotransferases (aspartate to oxaloacetate)
- Alanine aminotransferases (alanine to pyruvate)
How is liver disease monitored?
Measuring serum levels of alanine aminotransferase or aspartate aminotransferase
What is a significant energy yielding pathway in carnivores?
Oxidation of amino acids
Where do micro-organisms get their nitrogen from?
Scavenged from their environment
What are the 3 circumstances that amino acids undergo oxidative catabolism?
- Leftover amino acids from normal protein turnover are degraded
- Dietary amino acids that exceed body’s protein synthesis needs are degraded
- Proteins in the body are broken down to supply amino acids for catabolism when carbohydrates are in short supply
Describe the enzymatic hydrolysis of dietary proteins.
- Pepsin: proteins to peptides in stomach
- Trypsin/chymotrypsin: proteins & larger peptides to smaller peptide in small intestine
- Aminopeptidases/carboxypeptidases A and B: peptides to amino acids in small intestine
What maintains a steady supply of amino acids?
Digestion of dietary proteins in the intestine and the degradation of proteins within cells
What role does the stomach play in amino acid digestion?
Acidic environment and enzymes produce free amino acids and di/tri- peptides
What role does the intestine play in amino acid digestion?
Membrane bound proteins (aminopeptidases) degrade protein down further
What are cellular proteins targeted for destruction used to degrade?
- Misfolded proteins
- Foreign proteins
- Unwanted proteins
